U.S. patent number 7,711,464 [Application Number 12/020,102] was granted by the patent office on 2010-05-04 for steering system with lane keeping integration.
This patent grant is currently assigned to GM Global Technology Operations, Inc.. Invention is credited to Timothy W. Kaufmann.
United States Patent |
7,711,464 |
Kaufmann |
May 4, 2010 |
Steering system with lane keeping integration
Abstract
A system for steering a vehicle including: an actuator disposed
in a vehicle to apply torque to a steerable wheel; a driver input
device receptive to driver commands for directing the vehicle; and
a sensor for determining an intent of a driver and generating a
signal indicative thereof. The system also includes: a lane keeping
system for detecting a location of the vehicle relative to a lane
marker and generating a lane position signal indicative thereof; a
controller in operable communication with the actuator, the driver
input device, the first sensor, and the lane keeping system. The
controller provides a command to the actuator responsive to the
intent of the driver, the lane position, and a desired lane
position. The controller executes a lane keeping algorithm
consisting of a single control loop based on at least one of the
lane position and the lane position deviation.
Inventors: |
Kaufmann; Timothy W.
(Frankenmuth, MI) |
Assignee: |
GM Global Technology Operations,
Inc. (Detroit, MI)
|
Family
ID: |
39676877 |
Appl.
No.: |
12/020,102 |
Filed: |
January 25, 2008 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080189012 A1 |
Aug 7, 2008 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10865208 |
Jun 10, 2004 |
7510038 |
|
|
|
Current U.S.
Class: |
701/41 |
Current CPC
Class: |
B62D
1/286 (20130101); B62D 15/025 (20130101); B62D
15/029 (20130101); B60T 2201/087 (20130101); B60T
2201/082 (20130101); B60T 2201/08 (20130101) |
Current International
Class: |
B62D
6/00 (20060101) |
Field of
Search: |
;701/41,96,301
;340/903,436 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Black; Thomas G
Assistant Examiner: Louie; Wae
Attorney, Agent or Firm: Cantor Colburn LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of patent
application Ser. No. 10/865,208 filed Jun. 10, 2004.
Claims
What is claimed is:
1. A method for steering a vehicle comprising: receiving a lane
width value; determining a keep out distance as a function of at
least the lane width value; receiving a vehicle width value;
receiving a vehicle center to left lane marker distance; adding the
vehicle center to left lane marker distance to the keep out
distance and the vehicle width value; receiving a vehicle center to
right lane marker distance; subtracting the keep out distance and
the vehicle width value from the vehicle center to right lane
marker distance resulting in a right value; enabling a left warning
responsive to determining that the left value is greater than zero
and a left lane marker signal is available; and enabling a right
warning responsive to determining that the right value is less than
zero and a right lane marker signal is available.
2. The method of claim 1, wherein the vehicle width value is
divided by two to result in a one-half vehicle width value and
substituting the one-half vehicle width value for the vehicle width
value.
3. The method of claim 1, including receiving a vehicle speed value
and determining the keep out distance as a function of the lane
width value and the vehicle speed value.
4. The method of claim 1, wherein the method further comprises:
receiving a vehicle speed value; determining a keep out percentage
as a function of the lane width value and the vehicle speed value
and calculating the keep out distance as a product of the keep out
percentage and the lane width value.
5. The method of claim 1, wherein the method further comprises:
sending a torque warning signal comprising the left value
responsive to enabling the left warning; and sending a torque
warning signal comprising the right value responsive to enabling
the right warning.
6. The method of claim 5, wherein the method further comprises
effecting a torque force on a hand wheel responsive to receiving
the torque warning signal.
7. The method of claim 1, wherein the left warning and the right
warning are audio warnings.
8. The method of claim 1, wherein the left warning and the right
warning are visual warnings.
9. The method of claim 1, wherein the left warning and the right
warning are vibration warnings.
10. A steering system for a vehicle comprising: a sensor operative
to detect a left lane marker and a right lane marker; a processor
operative to: receive a lane width value; determine a keep out
distance as a function of at least the lane width value; receive a
vehicle width value; receive a vehicle center to left lane marker
distance; add the vehicle center to left lane marker distance to
the keep out distance and the vehicle width value; receive a
vehicle center to right lane marker distance; subtract the keep out
distance and the vehicle width value from the vehicle center to
right lane marker distance resulting in a right value; enable a
left warning responsive to determining that the left value is
greater than zero and a left lane marker signal is available; and
enable a right warning responsive to determining that the right
value is less than zero and a right lane marker signal is
available.
11. The system of claim 10, wherein the vehicle width value is
divided by two to result in a one-half vehicle width value and
substituting the one-half vehicle width value for the vehicle width
value.
12. The system of claim 10, wherein the processor is further
operative to receive a vehicle speed value and determine the keep
out distance as a function of the lane width value and the vehicle
speed value.
13. The system of claim 10, wherein the processor is further
operative to: receive a vehicle speed value; determine a keep out
percentage as a function of the lane width value and the vehicle
speed value and calculate the keep out distance as a product of the
keep out percentage and the lane width value.
14. The system of claim 10, wherein the processor is further
operative to: send a torque warning signal comprising the left
value responsive to enabling the left warning; and send a torque
warning signal comprising the right value responsive to enabling
the right warning.
15. The system of claim 14, wherein the system further comprises: a
motor operative to effect a torque force on a hand wheel responsive
to receiving the torque warning signal from the processor.
16. The system of claim 10, wherein the left warning and the right
warning are audio warnings.
17. The system of claim 10, wherein the left warning and the right
warning are visual warnings.
18. The system of claim 10, wherein the left warning and the right
warning are vibration warnings.
Description
BACKGROUND
The present disclosure relates generally to vehicle steering
control systems and, more particularly, to an electric power
steering system having a lane keeping function integrated
therewith.
A number of vehicle systems have been devised to assist the vehicle
in maintaining a central position within a driving lane. Generally,
a "lane keeping" system will include a device such as a video
camera that gathers information on the current position of the
vehicle, along with sensors for detecting certain dynamic state
variables of the vehicle. Changes in the curvature of the road path
is treated as unknown disturbances. Through the use of information
on the deviation of the vehicle from the center of the driving
lane, as well as the dynamic state variables of the vehicle, an
appropriate feedback indication is provided to the driver.
For example, the feedback indication could be in the form of an
audio signal, a visual signal, and/or a haptic signal to the
driver. Such a signal would alert the driver that a corrective
action may be required if the driver's intent is not to deviate
from the center of the driving lane. In addition to driver
feedback, the lane keeping system may also be integrated within the
steering system of the vehicle to provide a corrective input
thereto when a path deviation is detected. However, it may not
always be desirable for the lane keeping function to assume total
control over the steering but rather to assist the driver in
maintaining control of the vehicle's path in accordance with the
driver's intent.
Conventional lane keeping systems usually employ a camera system
and control system integrated with a steering system to provide a
lane keeping assist torque. In addition, such systems may employ
various means to evaluate the driver's intent to ascertain whether
a torque input in intentional or just a deviation of the vehicle
from a desired path. However, such systems are very complex,
involving multiple sensor systems and utilize multiple control
loops to maintain a lane keeping function. Accordingly, an
assistive lane keeping system is desired that provides operator
cues to assist an driver with lane keeping, yet may be configured
for autonomous operation that is less complex than existing
systems.
BRIEF SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies of the
prior art are overcome or alleviated by a system for steering a
vehicle comprising: an actuator disposed in a vehicle to apply
torque to a steerable wheel; a driver input device disposed in the
vehicle receptive to driver commands for directing the vehicle; and
a first sensor disposed in the vehicle for determining an intent of
a driver and generating a first signal indicative thereof. The
system also includes: a lane keeping system for detecting a
location of the vehicle relative to a lane marker and generating a
lane position signal indicative thereof and transmitting at least
one of a lane position signal and a lane position deviation; a
controller in operable communication with the actuator, the driver
input device, the first sensor, and the lane keeping system. The
controller provides a command to the actuator responsive to the
intent of the driver, the lane position, and a desired lane
position. The controller executes a lane keeping algorithm
consisting of a single control loop based on at least one of the
lane position and the lane position deviation.
Also disclosed herein in another exemplary embodiment, is a method
for steering a vehicle with an electric power steering system, the
method comprising: determining an intent of a driver of the
vehicle; ascertaining a location of the vehicle relative to a lane
marker and generating a lane position signal indicative thereof and
transmitting at least one of a lane position signal and a lane
position deviation; applying a lane keeping algorithm comprising a
single control loop based on at least one of the lane position and
the lane position deviation; and generating a command to an
actuator disposed in the vehicle to apply torque to a steerable
wheel, the command responsive to the intent of the driver, a
desired lane position, and the at least one of the lane position
and the lane position deviation.
In another exemplary embodiment disclosed herein is a system for
steering a vehicle with an electric power steering system
comprising: a means for determining an intent of a driver of the
vehicle; a means for ascertaining a location of the vehicle
relative to a lane marker and generating a lane position signal
indicative thereof and transmitting at least one of a lane position
signal and a lane position deviation to a controller; a means for
applying a lane keeping algorithm comprising a single control loop
based on at least one of said lane position and said lane position
deviation; and a means for generating a command to an actuator
disposed in the vehicle to apply torque to a steerable wheel, the
command responsive to the intent of the driver, a desired lane
position, and the at least one of the lane position and the lane
position deviation.
Further, disclosed herein in another exemplary embodiment is a
storage medium encoded with a machine readable computer program
code, the code including instructions for causing a computer to
implement the abovementioned method for steering a vehicle with an
electric power steering system.
Also disclosed herein in yet another exemplary embodiment is
computer data signal, the computer data signal comprising code
configured to cause a processor to implement the abovementioned
method for steering a vehicle with an electric power steering
system.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the exemplary drawings wherein like elements are
numbered alike in the several Figures:
FIG. 1 is a diagram depicting a vehicle in a lane with lane
markers;
FIG. 2 is a simplified block diagram of a lane keeping system in
accordance with an exemplary embodiment;
FIG. 3 is a diagram of a steering system in accordance with an
exemplary embodiment;
FIG. 4 is a simplified block diagram of an exemplary methodology
for lane keeping in accordance with an exemplary embodiment;
FIG. 5 is a diagram depicting a vehicle in a lane with lane
markers;
FIGS. 6 and 7 are block diagrams depicting other exemplary
embodiments of a lane keeping system.
FIGS. 8a and 8b are block diagrams depicting an alternate exemplary
embodiment of a lane keeping system; and
DETAILED DESCRIPTION
Disclosed herein is a lane keeping system integrated with an
electric steering system. Existing systems commonly employ multiple
control loops to maintain stability. Primarily they include lane
position, lane curvature and heading angle control loops. Multiple
control loops are often necessitated by low bandwidth of sensors
and/or camera system. The lane keeping system of an exemplary
embodiment employs a single control loop with lead-lag compensation
to provide stable operation with reduced latency with a low
bandwidth sensor system and camera. Advantageously, the lane
keeping system of an exemplary embodiment operates with a single
(only one) lane keeping control loop in a stable configuration
reducing complexity, integration effort, and cost relative to
existing systems.
The present invention may be utilized in various types of vehicles
employing electronic steering or steer by wire systems or with the
addition of a electric motor on an hydraulic steering system. A
preferred embodiment of the invention, by way of illustration is
described herein as it may be applied to an automobile employing an
electric power steering system. While a preferred embodiment is
shown and described by illustration and reference to an automobile
steering system, it will be appreciated by those skilled in the art
that the invention is not limited to the automobiles alone by may
be applied to all vehicles employing electronic steering systems,
steer by wire systems, or even hydraulically controlled steering
systems where a lane keeping command may be integrated with
existing steering commands.
Referring now to FIG. 1, there is depicted a vehicle 1 in a lane
with various lane markers 2 to the left, right, (there is no lane
center marker, it is calculated). The lane keeping system provides
two modes of operation, a helper or assist mode, and an autonomous
mode. In helper mode the operator is hands on, and the system
provides audio warning(s) and/or tactic feedback warnings (for
example, to simulate the noise/feel of a rumble strip) on the side
of the vehicle that indicates the vehicle is approaching a lane
marker. The warnings and cues may be overridden by activation of a
turn signal indicating operator intent to change lanes. For
example, in the helper (assist) mode, because application of torque
nudges can cause the vehicle 1 to dart back and forth between lane
markers 2 if the driver were not controlling the steering wheel, it
desirable to determine if the drivers is, in fact holding the
wheel. If so, then a torque nudge may be applied. As disclosed at a
later point herein, a pressure/force sensor may be employed to
determine if the driver is controlling the steering wheel.
In Autonomous mode the system is enabled after the operator has
maintained the vehicle 1 within a tolerance band from the lane
center for a selected period. The lane keeping system warns the
operator of an impending engagement of the autonomous mode with a
chime, and then engages. The autonomous mode maintains the vehicle
1 in the lane and requires no operator input to control the vehicle
1. In an exemplary embodiment, the lane keeping system employs a
left marker as the primary marker but can readily transition to the
right marker or a center marker if the left marker cannot be
identified. For example, in the autonomous mode, the torque sensor
is used for determining driver intent. In this mode, the driver may
want to make a correction and/or over ride the lane keeping system
100. So, when the driver inputs a torque greater than about, for
example, 0.25 Nm, the lane keeping system 100 transitions to the
helper (assist) mode. When the driver has completed his correction
the lane keeping system 100 transitions back to autonomous mode
when the driver is within 0.5 meters of the lane center, for a
duration of 5 seconds, when both of these conditions have been met
the lane keeping system transitions back to the autonomous
mode.
Continuing with FIG. 1, the lane keeping system can be configured
to operate with either a keep out functionality, or a constant
correction from center (with a dead band) functionality. With the
keep out functionality, the lane keeping system responds only when
the vehicle 1 is within some predefined distance from a boundary
line. When the vehicle 1 approaches a boundary line, the system
activates a visual warning lamp, audible warnings, and provides a
torque nudge to the operator via the steering wheel in the
direction away from the lane boundary line. Similarly, with the
correction from center functionality, when the vehicle 1 deviates
from the center of the lane by a selected offset, the lane keeping
system provides a visual warning and torque nudge.
In an exemplary embodiment, the lane keeping system is enabled for
a selected speed range of the vehicle 1. The system may be
configured to operate only over a small range of total system
authority and rates. In an exemplary embodiment, the lane keeping
system 100 utilizes ten percent of total system control authority.
It will be appreciated that other configurations are
conceivable.
Referring also to FIG. 2, there is shown a simplified block diagram
of a lane keeping system 100 in accordance with an exemplary
embodiment. A lane departure warning system 110 including a lane
tracking system 112 is integrated with an electric steering system
40. The lane tracking system 112 may include but not be limited to,
a camera system for detection of lane markers/markings and
computing a lane position signal 114. The lane keeping system 100
is also optionally integrated with auxiliary sensors such as a
global positioning system (GPS with map navigation system) 120 and
dynamic sensors 130 such as, but not limited to a yaw rate sensor.
The lane keeping system 100 is also integrated with various
controls 140 and enunciators 150 to provide indications and
feedback to the operator.
The integration of GPS may be employed for route planning and
navigation. Furthermore, GPS may be employed to inform the lane
keeping system 100 when the vehicle 1 is approaching a defined
point in the roadway, such as, an exit, but not limited thereto.
Under such conditions, the lane keeping system 100 can identify the
type of lane marker 2, e.g., dashed or solid. If, for example, the
right line is solid, it may be inferred that the vehicle 1 is in
the right most lane. The lane keeping system 100 would switch to
the left line if the route planning indicates that the intention is
to continue along the present course. This switch will ensure that
the lane keeping system 100 does not direct the vehicle 1 down the
exit. It; on the other hand, it is intended to take the exit, the
lane keeping system 100 would be in the right lane (if it is an
right exit) and track the right most lane marker 2, to direct the
vehicle 1 on to the exit.
In an exemplary embodiment, the lane keeping system also includes a
driver attention monitoring device 170. The driver attention
monitoring device 170 facilitates the lane keeping system 100
taking action when the operator's attention is not focused on the
roadway. The driver attention monitoring device 170 informs the
lane keeping system 100 that the driver is at some level of
drowsiness/inattentiveness. The driver attention monitoring device
170 includes, but is not limited to a camera system with infrared
flood (or equivalent apparatus) to monitor the status of the
operator, in particular, an operator's eyes. In one exemplary
embodiment the driver attention monitoring device 170 monitors the
operator's eye(s) to ascertain a percentage eye closure. The lane
keeping system 100 may then employ such a determination by to take
action and provide warnings to the operator. For example, the
driver attention monitoring device 170 may be employed as an
indicator when the driver has taken their eyes off the roadway for
a duration exceeding a selected time.
When the driver attention monitoring device 170 ascertains that a
driver is inattentive, the lane keeping system 100 responds with
torque nudges, if the driver's hands are on the steering wheel 26
(helper (Assist) mode). In addition, audible (raising and lowering
of the radio may be part of this feature) and visual warnings may
be activated along with steering wheel buzz (as described herein).
If the driver does not take control of the vehicle 1 or the driver
attention monitoring device 170 does not indicate that the driver
is awake, the lane keeping system may enter autonomous mode. The
system may communicate to other systems in the vehicle 1 that the
driver is not responding. The lane keeping system 100 may be
integrated with other systems such as speed control and steering to
slow the vehicle 1, or pull off to the side of the road and stop.
Moreover in vehicles 1 equipped with OnStar.RTM. type capability,
the OnStar.RTM. system may be activated. Advantageously, such
systems may be highly beneficial for cases of medical emergencies
and the like.
Referring to FIG. 3, reference numeral 40 generally designates a
motor vehicle electric power steering system suitable for
implementation of the disclosed embodiments. Examples of other
steering systems that may be suitable for implementation of the
disclosed embodiments may be found in commonly assigned: U.S. Pat.
No. 6,122,579 to Collier-Hallman et al.; U.S. Pat. No. 5,704,446 to
Chandy et al.; U.S. Pat. No. 5,719,766 to Bolourchi et al.; U.S.
Pat. No. 5,668,722 to Kaufmann et al.; U.S. patent application Ser.
No. 10/165,037 to Patankar; U.S. Pat. No. 6,363,305 to Kaufmann et
al.; and U.S. Pat. No. 6,370,460 to Kaufmann et al. the disclosures
of which are incorporated by reference herein in their
entirety.
Returning with FIG. 3, the steering mechanism 36 is a
rack-and-pinion type system and includes a toothed rack (not shown)
within housing 50 and a pinion gear (also not shown) located under
gear housing 52. As the operator input, hereinafter denoted as a
steering wheel 26 (e.g. a hand wheel and the like) is turned, the
upper steering shaft 29 turns and the lower steering shaft 51,
connected to the upper steering shaft 29 through universal joint
34, turns the pinion gear. Rotation of the pinion gear moves the
rack, which moves tie rods 38 (only one shown) in turn moving the
steering knuckles 39 (only one shown), which turn a steerable
wheel(s) 44 (only one shown).
Electric power steering assist is provided through the control
apparatus generally designated by reference numeral 24 and includes
the controller 16 and an electric machine 46 in this instance a
brushless DC motor hereinafter denoted motor 46. The controller 16
is powered by the vehicle power supply 10 through line 12. The
controller 16 receives a vehicle speed signal 14 representative of
the vehicle velocity. Steering angle is measured through position
sensor 32, which may be an optical encoding type sensor, variable
resistance type sensor, or any other suitable type of position
sensor, and supplies to the controller 16 a position signal 20.
Motor velocity may be measured with a tachometer and transmitted to
controller 16 as a motor velocity signal 21. A motor velocity
denoted .omega..sub.m may be measured, calculated or a combination
thereof. For example, the motor velocity .omega..sub.m may be
calculated as the change of the motor position .theta. as measured
by a position sensor 32 over a prescribed time interval. For
example, motor speed .omega..sub.m may be determined as the
derivative of the motor position .theta. from the equation
.omega..sub.m=.DELTA..theta./.DELTA.t where .DELTA.t is the
sampling time and .DELTA..theta. is the change in position during
the sampling interval. Alternatively, motor velocity may be derived
from motor position as the time rate of change of position. It will
be appreciated that there are numerous well-known methodologies for
performing the function of a derivative.
As the steering wheel 26 is turned, torque sensor 28 senses the
torque applied to the steering wheel 26 by the vehicle operator.
The torque sensor 28 may include a torsion bar (not shown) and a
variable resistive-type sensor (also not shown), which outputs a
variable torque signal 18 to controller 16 in relation to the
amount of twist on the torsion bar. Although this is the preferable
torque sensor, any other suitable torque-sensing device used with
known signal processing techniques will suffice. In response to the
various inputs, the controller sends a command 22 to the electric
motor 46, which supplies torque assist to the steering system
through worm 47 and worm gear 48, providing torque assist to the
vehicle steering.
It should be noted that although the disclosed embodiments are
described by way of reference to motor control for electric
steering applications, it will be appreciated that such references
are illustrative only and the disclosed embodiments may be applied
to any motor control application employing a motor, e.g., steering,
valve control, and the like. Moreover, the references and
descriptions herein may apply to many forms of parameter sensors,
including, but not limited to torque, position, speed and the like.
It should also be noted that reference herein to electric machines
including, but not limited to, motors, or more specifically
switched reluctance motors, hereafter, for brevity and simplicity,
reference will be made to motors only without limitation.
In the control system 24 as depicted, the controller 16 utilizes
the torque, position, and speed, and like, to compute a command(s)
to deliver the required output power. Controller 16 is disposed in
communication with the various systems and sensors of the motor
control system. Controller 16 receives signals from each of the
system sensors, quantifies the received information, and provides
an output command signal(s) in response thereto, in this instance,
for example, to the motor 46. Controller 16 is configured to
develop the necessary voltage(s) out of inverter (not shown), which
may optionally be incorporated with controller 16 and will be
referred to herein as controller 16, such that, when applied to the
motor 46, the desired torque or position is generated. Because
these voltages are related to the position and speed of the motor
46 and the desired torque, the position and/or speed of the rotor
and the torque applied by an operator are determined. A position
encoder is connected to the steering shaft 51 to detect the angular
position .theta.. The encoder may sense the rotary position based
on optical detection, magnetic field variations, or other
methodologies. Typical position sensors include potentiometers,
resolvers, synchros, encoders, and the like, as well as
combinations comprising at least one of the forgoing. The position
encoder outputs a position signal 20 indicating the angular
position of the steering shaft 51 and thereby, that of the motor
46.
Desired torque may be determined by one or more torque sensors 28
transmitting torque signals 18 indicative of an applied torque. An
exemplary embodiment includes such a torque sensor 28 and the
torque signal(s) 18 therefrom, as may be responsive to a compliant
torsion bar, T-bar, spring, or similar apparatus (not shown)
configured to provide a response indicative of the torque applied.
In addition, steering wheel pressure may be determined by one or
more force/pressure sensors 30 at the steering wheel 26. The
force/pressure sensors 30 generate force/pressure signals 31
indicative of an applied pressure to steering wheel 26, which are
transmitted to the controller 16.
Optionally, a temperature sensor(s) 23 located at the electric
machine 46. Preferably, the temperature sensor 23 is configured to
directly measure the temperature of the sensing portion of the
motor 46. The temperature sensor 23 transmits a temperature signal
25 to the controller 16 to facilitate the processing prescribed
herein and compensation. Typical temperature sensors include
thermocouples, thermistors, thermostats, and the like, as well as
combinations comprising at least one of the foregoing sensors,
which when appropriately placed provide a calibratable signal
proportional to the particular temperature.
The position signal 20, velocity signal 21, and a torque signal(s)
18 among others, are applied to the controller 16. The controller
16 processes all input signals to generate values corresponding to
each of the signals resulting in a rotor position value, a motor
speed value, and a torque value being available for the processing
in the algorithms as prescribed herein. Measurement signals, such
as the abovementioned are also commonly linearized, compensated,
and filtered as desired or necessary to enhance the characteristics
or eliminate undesirable characteristics of the acquired signal.
For example, the signals may be linearized to improve processing
speed, or to address a large dynamic range of the signal. In
addition, frequency or time based compensation and filtering may be
employed to eliminate noise or avoid undesirable spectral
characteristics.
In order to perform the prescribed functions and desired
processing, as well as the computations therefore (e.g., the lane
keeping and steering functions, control algorithm(s), and the
like), controller 16 may include, but not be limited to, a
processor(s), computer(s), DSP(s), memory, storage, register(s),
timing, interrupt(s), communication interface(s), and input/output
signal interfaces, and the like, as well as combinations comprising
at least one of the foregoing. For example, controller 16 may
include input signal processing and filtering to enable accurate
sampling and conversion or acquisitions of such signals from
communications interfaces. Additional features of controller 16 and
certain processes therein are thoroughly discussed at a later point
herein.
As exemplified herein and disclosed above one such process may be a
lane-keeping algorithm. Controller 16 receives various input
signals including, but not limited to, those identified above, to
facilitate such processing and may provide one or more output
signals in response. Also received by the controller 16 are a
variety of implementation specific parameters, signals and values
for initialization and characterization of the prescribed processes
and to identify various states of the processes herein.
Controller 16 may also be interfaced with a communications bus 160
to facilitate communications in the vehicle 1. In an exemplary
embodiment a serial communications bus, denoted CAN is employed.
The CAN enables communications with the lane departure warning
system 110 and an optional GPS and map navigation system 120. It
will be appreciate that the communications bus 160 may be employed
for communication with various sensors, systems, actuators and the
like. For example, in an exemplary embodiment, the communications
bus provides communications between the lane tracking system lane
departure warning system 110 and steering system 40. More
particularly, the communications bus 160 is employed to transmit
lane position to the steering system 40 and transmit various
vehicle parameters to the lane departure warning system 110. The
GPS may use NEMA-0183 RS-232 bus utilized in Marine Systems or
similar equivalent communications interfaces.
Turning now to the lane departure warning system 110 and more
particularly the lane keeping system 112, in an exemplary
embodiment the lane keeping system 112 employs an optical sensor
114 and image processing system 116 that detects and tracks lane
markings 2. When an unplanned or uninitiated lane departure is
detected, a warning signal is generated. The warning signal
indicates on which side of the vehicle 1/lane the departure is
occurring. In addition, the lane keeping system 112 transmits data
regarding the position of the vehicle 1 in the lane and an estimate
of road curvature. In an exemplary embodiment, the AutoVue.TM.
system form Iteris.TM. Inc. is configured for application as the
lane keeping system 112, however other systems with similar
capabilities are feasible. The lane keeping system employs a
ruggedized, embedded image capture and analysis computer. An
imaging sensor creates a two dimensional digitized image of the
area ahead of the vehicle 1. The computer provides algorithms for
analysis of the captured image information to ascertain desired
information including, but not limited to lane position, deviation
from desired lane position, and roadway curvature.
In an exemplary embodiment, the lane keeping system 112 includes an
interface to the communications bus 160 for interfacing with the
vehicle 1 and more particularly the steering system 40. The frame
rate, response time, and data rate of the lane keeping system 112
and communications bus 160 is configured to ensure a latency of
less than about 44 milliseconds for communication of information to
the steering system 40.
Turning now to FIG. 4 a simplified block diagram of an illustrative
system and methodology for lane keeping in accordance with an
exemplary embodiment is depicted. Similar configurations are
employed for applying torque commands to the steering system
responsive to the Lane keeping system 100. In the helper or assist
mode, audible warning(s), visual enunciations (e.g., telltale on
the instrument panel) and/or tactile feedback warnings are
generated (for example, to simulate the noise/feel of a rumble
strip) or torque disturbances (nudges) or torque resistance on the
side of the vehicle 1 that indicates the vehicle 1 is approaching a
lane marker. Tactile feedback may be achieved with a separate
oscillatory actuator, for example, a motor with and eccentric
weight applied to the steering wheel of the vehicle 1 or via
existing steering actuators. The warnings and cues may be
overridden by activation of a turn signal indicating operator
intent to change lanes. In the autonomous mode, the lane keeping
system 100 warns the operator with an audible warning of an
impending engagement of the autonomous mode, and then engages,
providing steering corrections to maintain the vehicle 1 on the
marked roadway. Similarly, the lane keeping system 100 may be
employed to provide feedback to the operator in instances when a
lane change is intended but the operator has not indicated the
intention by employing a turn signal. In an exemplary embodiment,
the lane keeping system employs a left marker 2 as the primary lane
marker 2 but can readily transition to the right lane marker 2 if
the left lane marker 2 cannot be identified. Such transitions would
be automated and essentially transparent to the operator. In an
exemplary embodiment, the lane keeping system may also maintain an
estimate of the lane width. Lane width is calculated when both left
and right lane markers 2 are present. When one of the lane markers
2 cannot be found, the lane width is maintained and not
recalculated until both markers 2 are present once again.
Transitions between the helper mode and autonomous mode may be
operator selected or automated based on determinations of driver
intent. For example, engagement of a turn signal is employed as an
indication of driver intent to turn or change lanes. In addition,
in an exemplary embodiment transitions application of a torque to
the steering wheel 26 for a selected duration is utilized as an
indication of driver intent to make a driver input e.g., turn or
change lanes. Under such conditions, the lane keeping system 100
automatically transitions from the autonomous mode to the helper
mode. Conversely, in one embodiment, when in the helper mode,
maintaining the vehicle 1 within a selected position tolerance in
the lane for a selected duration enable transitioning to the
autonomous mode.
Similarly, under selected conditions, steering wheel force/pressure
is employed as an indicator that the operator intends to be making
steering corrections, and therefore is employed for selected mode
transitions. In exemplary embodiment transitions the presence of
steering wheel force/pressure for a selected duration is utilized
as an indication of driver intent to make a driver input e.g., turn
or change lanes. Likewise, in another exemplary embodiment, under
selected conditions, steering wheel rate or torque rates may be
employed as an indicator that the operator intends to be making
steering corrections, and therefore is employed for selected mode
transitions. Under such conditions, the lane keeping system 100
automatically transitions from the autonomous mode to the helper
mode. It will be appreciated that determination of driver intent is
a note necessarily deterministic and that turn signals, torque
applied to the steering wheel, and steering wheel force/pressure
are only indicators of driver intent. Therefore, each of the
various sensors alone or in combination may be employed to
ascertain driver intent with varying degrees of accuracy.
Returning to FIG. 4, a steering torque control algorithm 200 is
depicted with the addition of a lane-keeping algorithm 300. In an
exemplary embodiment, controller 16 of the steering system 40
executes the algorithms of the lane keeping functions as well as
the algorithms for the steering functions. The lane tracking system
112 tracks lane markers 2 generally on the roadway to ascertain a
lane position. The lane tracking system 112 transmits various
signals to the lane keeping algorithm 300, including, but not
limited to a signal indicative of lane position 118 and a status
and/or validity of the data 119. The lane-keeping algorithm 300
receives lane position signal 118, vehicle status signals, an
enable signal as well as vehicle parameters such as, but not
limited to, vehicle speed, torque and optionally yaw rate. The
lane-keeping algorithm 300 formulates a lane keeping command 320
that is combined with the vehicle steering system motor torque
command 220 of the steering control algorithm 200 to formulate a
composite steering torque command 222 that is ultimately directed
to the steering motor 46.
Turning now to FIG. 5 as well, in an exemplary embodiment, to
maintain stability of the lane-keeping system 100, and more
specifically the lane keeping algorithm 300 employs only a single
control loop based on lane position e.g., 118 and/or lane position
deviation as an input to a steering torque control algorithm 200.
Conversely, existing systems generally utilize multiple control
loops to ensure stability. Advantageously, a single control loop is
simpler to implement and often more readily tuned and optimized to
achieve desired performance of the lane keeping system 100.
As stated above, the lane keeping algorithm 300 receives a signal
indicative of a position 118 for comparison with a reference 302
e.g., lane center, and the like, to ascertain a lane deviation 304.
Alternatively, the lane keeping system 112 could compute a lane
deviation 304 from a selected reference and transmit the deviation
to the lane keeping algorithm 300. While it is described herein
that the lane keeping algorithm 300 performs a computation to
ascertain a lane position deviation 304, it will be appreciated
that there are numerous means of implementation for ascertaining
the deviation of the vehicle 1 from a selected reference lane
position 302, all of which should be considered within the scope of
the claims. Continuing with the lane keeping algorithm 300 the lane
position deviation is applied to a selected loop gain 306 to
ultimately formulate a lane keeping command 320 for the steering
algorithm 200.
It will be appreciated that to maintain stability of the
lane-keeping system 100, the lane keeping control algorithm 300 may
include a compensator 308 to address the bandwidth and/or dynamic
characteristics of various system elements. For example, based on
the update rates and latency of the lane departure warning system
100 e.g. cameras 114 and associated processing 116, additional
compensation may be required. In an exemplary embodiment a lead-lag
type compensator 308 is coupled in the lane keeping motor torque
control loop to provide sufficient phase lead to maintain
stability. Furthermore, in an exemplary embodiment, the compensator
308 is configured to provide stability of the lane keeping system
100 at sufficient gains to achieve an overall lane keeping loop
bandwidth greater than about 3 Hz, preferably greater than about 5
Hz. Once again, while a particular implementation is described as
an exemplary embodiment, it will be appreciated that other
configurations may be possible and within the scope of the
claims.
It will be appreciated that the lane keeping control algorithm 300
and/or steering torque control algorithm 200 may optionally include
one or more limiters 310 to address clamping the magnitude of the
contribution to the composite steering torque command 222 from the
lane keeping command 320. For example in an exemplary embodiment a
limiter 310 constrains the maximum contribution to no more than 5
Newton-meters (Nm) of bias torque to the steering algorithm 100 to
limit lane keeping inputs to the steering system 40.
It will be appreciated that while the disclosed embodiments refer
to a configuration utilizing gain e.g. 306 or scaling in
implementation, various alternatives will be apparent. It is well
known that such gain as depicted may be implemented employing
numerous variations, configurations, and topologies for
flexibility. For example, the processes described above could
employ in addition to or in lieu of scaling gains, look-up tables,
direct algorithms, parameter scheduling or various other
methodologies, which may facilitate execution of the desired
functions, and the like, as well as combinations including at least
one of the foregoing.
In a similar manner, it will be appreciated that the compensator
308 may be implemented employing a variety of methods including but
not limited to passive, active, discrete, digital, and the like, as
well as combinations including at least one of the foregoing. More
over the compensator 308 as disclosed are illustrative of an
exemplary embodiment and is not limiting as to the scope of what
may be employed. It should also be noted, that in an exemplary
embodiment compensator 308 could also take the form of simple
scaling, scheduling look-up tables and the like as desired to
tailor the content or spectral content of the position signals
employed as compensation. Such configuration would depend on the
constraints of a particular control system and the level of
compensation required to maintain stability and/or achieve the
desired control loop response characteristics.
Turning now to the particulars of selecting the proper transfer
function for the compensator 308. In an exemplary embodiment, the
compensator 308 is depicted with a first-order lead-lag exhibiting
a substantially constant gain at frequencies above a cutoff. An
advantageous feature of the exemplary embodiment disclosed herein
is that it provides opportunity to tune the performance of the lane
keeping control algorithm 300 independent of the steering algorithm
200 and ultimately the steering system 40 to satisfy a variety of
desired characteristics. Furthermore, it will be appreciated that
the compensator 308 is configured as illustrated based on the
dynamic characteristics of the components e.g., lane departure
warning system 110 for a given implementation. Utilization of
higher bandwidth components e.g., lane keeping system 100,
processing, actuators 46 and the like as well as combinations
including any of the foregoing, may readily yield simplification or
elimination of compensation elements yet still permit maintaining
stability of the lane keeping system 100. It is also noteworthy to
appreciate that increasing the bandwidth of the steering algorithms
200, lane keeping system 100 and/or lane keeping algorithm 300, or
overall steering system 40 may also improve the total dynamic
characteristics of the of the lane keeping system 100. As a result,
a compensation means such as compensator 308 may be designed so
that increases the bandwidth of the steering algorithms 200, lane
keeping algorithms 300, and/or the entire steering system 40 also
changes the dynamic characteristics of the lane keeping system 100.
Once again, bandwidth increases in one part of the system may
provide for improved performance and/or relaxed requirements for
other portions of the system.
FIG. 5 illustrates an example of a vehicle operating on a roadway.
A vehicle 501 has a vehicle center 503 and a vehicle width 515. The
roadway includes a left marker 505 and a right marker 507. A
distance from the vehicle center 503 to the left marker 505 is 509
and a distance from the vehicle center 503 to the right marker 507
is 511. Keep out zones 513 are illustrated on the right and left of
the vehicle 501.
As the vehicle 501 moves along the roadway, the roadway narrows.
Because the roadway narrows, the keep out zones 513 narrow. FIGS.
6, 7, 8a, and 8b illustrate a block diagram of an exemplary method
of operation of the lane tracking system 112 (of FIG. 1).
Referring to FIG. 6, a keep out distance that defines the keep out
zones 513 is defined by receiving a lane width value 602 and a
vehicle speed value 604. The lane width value 602 and the vehicle
speed value 604 are used in a function 601 that defines the keep
out distance 606. In some embodiments, the function 601 may be used
to create a keep out distance table that is used to determine the
keep out distance thereby decreasing processing time. By using the
function of the lane width value 602 and the vehicle speed value
604, the keep out distance 606 may be adjusted when the lane width
changes and when the vehicle speed changes.
FIG. 7 illustrates an alternate method for determining the keep out
distance. The lane width value 602 and the vehicle speed value 604
are used in a function to define a keep out percentage in block
701. In some embodiments, the function 701 may be used to create a
keep out percentage table that is used to determine the keep out
percentage thereby decreasing processing time. The lane width value
602 and the keep out percentage are multiplied to result in the
keep out distance 606.
FIG. 8a further illustrates a method for lane keeping. A vehicle
width is received in block 601 and divided by 2 to result in a
one-half vehicle width value. The vehicle center to the left marker
distance 509 is received at block 808, and the keep out distance
606 is received at block 606. The vehicle center to the left marker
distance 509, the one-half vehicle width value, and the keep out
distance 606 are added to result in a left value received in a u1
input of block 603. Block 603 also receives a signal at a u2 input
that indicates whether the left lane marker 505 is available. For
example, if the camera system 114 that detects the left lane marker
505 has a clear picture of the left lane marker 505, the signal
will be 1, whereas if the camera does not detect the left lane
marker 505, the signal will be 0. In the block 603. logic is used
to determine if u1>0 and if u2=1. If the conditions are met, 603
outputs a 1 value. If u2=0, or any other else condition exists,
block 603 outputs a 0 value. The outputs merge in block 619 and are
operative to enable a left warning in block 816 if the output from
the block 619 is 1.
The vehicle center to the right marker distance 511 is received at
block 812. The keep out distance 606 and the one-half vehicle width
value are subtracted from the vehicle center to the right marker
distance 511 resulting in a right value that is received by block
605 in a u1 input. A u2 input to block 605 indicates whether the
right lane marker 505 is detected. In the block 605, logic is used
to determine if u1<0 and if u2=1. If the conditions are met, 605
outputs a 1 value. If u2=0, or any other else condition exists,
block 605 outputs a 0 value. The outputs merge in block 621 and are
operative to enable a right warning in block 818 if the output from
the block 621 is 1.
Referring to FIG. 8b, the enable left warning in block 816 is
received in a block 623 at a u1 input and the enable right warning
in block 818 is received in the block 623 at a u2 input. In the
block 623, logic is used to determine whether the u1 input value or
the u2 input value are 1. If the u1 input value is 1, the left
value is input as "B" in a block 625. Elseif the u2 input is 1, the
right value is input as "A" in a block 627. All other inputs are
else and output as a 0 value in a block 629. The outputs from the
blocks 625, 627, and 629 are merged to result in a torque warning
signal 820.
The torque warning signal 820 may be processed with a gain value to
send a signal to a motor that is operative to impart a torque
disturbances (nudges) or torque resistance on the side of the
vehicle 501 that indicates the vehicle 501 is approaching a lane
marker.
The enable left warning 8 and the enable right warning 9 may be
used to actuate audible warning(s), visual enunciations (e.g.,
telltale on the instrument panel) and/or tactile feedback warnings
are generated (for example, to simulate the noise/feel of a rumble
strip).
It should also be noted that the figures may depict additional
elements, connections, interconnections and the like as may be
employed for implementation of a selected control configuration.
For example, transport delays may be employed to ensure that date
time coherency is addressed. Likewise, scaling may be employed to
address unit conversions and the like, and limiters may be employed
to clamp selected signals.
As will be appreciated, the disclosed invention can be embodied in
the form of computer or controller implemented processes and
apparatuses for practicing those processes. The present invention
can also be embodied in the form of computer program code
containing instructions embodied in tangible media 13, such as
floppy diskettes, CD-ROMs, hard drives, or any other
computer-readable storage medium, wherein, when the computer
program code is loaded into and executed by a computer or
controller, the computer becomes an apparatus for practicing the
invention. The present invention may also be embodied in the form
of computer program code or signal 15, for example, whether stored
in a storage medium, loaded into and/or executed by a computer or
controller, or transmitted over some transmission medium, such as
over electrical wiring or cabling, through fiber optics, or via
electromagnetic radiation, wherein, when the computer program code
is loaded into and executed by a computer, the computer becomes an
apparatus for practicing the invention. When implemented on a
general-purpose microprocessor, the computer program code segments
configure the microprocessor to create specific logic circuits.
It will be appreciated that the use of first and second or other
similar nomenclature for denoting similar items is not intended to
specify or imply any particular order unless otherwise stated.
While the invention has been described with reference to a
preferred embodiment(s), it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *